Safe hypothermic storage of isolated livers is currently limited to less than 24 hours. Increased O2 delivery by a hemoglobin based oxygen carrier during cooling may reduce hypoxia related endothelial cell damage and enhance organ survival. We will compare hepatic biochemical and physiological function during normothermic (37 degree C) perfusion of livers that have been hypothermically stored for 24 hours in the presence of current storage solutions and red blood cell substitute made up of ultrapure polymerized bovine hemoglobin. Donor livers, obtained from normal fed rats, will be assessed for biliary excretion, O2 utilization, production of glucose, lactate, amino acid N, urea N, release of K+ and tissue injury enzymes (lactodehydrogenase, transaminases), residual hepatic glycogen, ATP content and histological changes to delineate the extent of hepatocellular injury with each solution. This will define the optimal conditions for extending hypothermic preservation of livers (and presumably other organs) beyond 24 hours with the oxygen carrier.